Of the 25 million people who are hearing impaired, 85% suffer from sensorineural hearing loss (SNHL), a loss of hearing due to decreased hearing nerve function. There are various forms of inner ear disorders causing SNHL, including Meniere's disease, viral labyrinthitis, perilymph fistula, otosyphilis, and congenial or hereditary deafness. Sensorineural hearing loss is generally accompanied by ear fullness, tinnitus and disturbance of balance. A number of medical, dietary and surgical treatments are available for SNHL. See, e.g., Hicks and Wright III (1991) Indiana Medicine 84(8): 450-544.
Autoimmune sensorineural hearing loss (ASNHL) has been considered by some as a separate entity of SNHL and by others as a cause for various forms of SNHL. ASNHL is characterized by progressive unilateral or bilateral deafness that, in its incipient stages, may fluctuate or become sudden and profound. The symptoms of ASNHL are quite similar to other forms of SNHL. ASNHL is believed to occur when the body's immune system attacks and progressively destroys the inner ear. The pathogenesis of ASNHL includes vasculitis of vessels supplying the inner ear, autoantibodies directed against inner ear antigenic epitopes or cross-reacting antibodies. See, e.g., Hicks and Wright III (1991) and U.S. Pat. No. 5,422,282 to Harris.
A traditional line of therapy for ASNHL has been oral or parenteral administration of various immunosuppressants including steroids, cytotoxic drugs (such as cyclophosphamide) or methotrexate. Steroid therapy is associated with various side effects, such as weight gain, facial puffiness and constitutional changes (Sismanis et al., Laryngoscope 104: 932-934, 1994). Cyclophosphamide has dramatic adverse effects as well, e.g., severe nausea and vomiting, thrombocytopenia, leukopenia and hemorrhagic cystitis (Sismanis et al., 1994). Methotrexate appears to be less toxic. However, large scale studies are required to confirm the efficacy of methotrexate for treating ASNHL (Sismanis et al., 1994). Plasmapheresis has been suggested as an alternative therapy for patients who are intolerant to steroids and/or cyclophosphamide, but has been considered as impractical (Luetje Laryngoscope 99: 1137-1146, 1989).
Despite the different therapies currently available, there is a need for more effective methods of treating ASNHL with fewer accompanying side effects. The present invention provides effective methods for treating ASNHL by oral administration of a human immunoglobulin preparation.